The Big Four: Criteria for Fabric Mask Materials for COVID

Spunbond nonwoven polypropylene for masks

This deep dive post looks into the “Big Four” criteria evaluated in preliminary assessments of fabric mask materials: 1) material characteristics, 2) breathability, 3) water-resistance, and 4) disinfection options. More specifically, we focus on spunbond nonwoven polypropylene (NWPP), which is commonly used in commercial face masks. Here we take a more in-depth look at the 4 preliminary criteria considered when evaluating potential sources of spunbond NWPP.

1. Mask Material Characteristics & Sourcing

MakerMask designs use community-sourced 100% spunbond nonwoven polypropylene. Although ideal medical grade NWPP is not currently available for community use, spunbond NWPP is available at different weights and grades for other household and/or commercial purposes, such as reusable grocery bags, some craft fabrics (e.g., Smart-Fab and Oly-Fun), and some sew-in interfacing.

Infographic showing some of the key characteristics of spunbond nonwoven polypropylene (NWPP) for masks

Standard measurements of fabric weight (gsm or oz/yd²)

Fabrics may be characterized in a number of different ways, a standard measurement for fabric weight is grams per square meter (gsm) or ounces per square yard (oz/yd²). Although either set of units can be used (e.g., 50 gsm = 1.47 oz/yd², 100 gsm = 2.95 oz/yd²), we will use gsm throughout our discussions. For those more familiar with ounces and yards, check this Handy Conversion Tool.

Although medical grade NWPP (20 – 25 gsm) is used in commercial masks and respirators, for ethical reasons these materials are currently reserved for manufacturers that best meet medical, legal, and regulatory standards. Given that these medical grade NWPP materials are not widely available to the public at this time, the preferred sources of spunbond NWPP for use in community masks has been reusable grocery bags (~70 – 100 gsm). However, NWPP from reusable grocery bags is not readily available to sewists and mask makers by the yard. As a result, spunbond NWPP that is more commonly available by the yard (i.e., that used in clothing, textiles, crafting, and upholstery applications) is being investigated for suitability for use in masks. Recent testing results of the breathability, filtration, and fluid resistance of spunbond NWPP used in some craft applications (i.e., SmartFab Backgrounds, ~65 – 70 gsm) suggests it may be a good choice for use in community masks.

Polypropylene: How to Choose? (image) Shows a stick figure leaning against a big question mark with detailed image of spunbond nonwoven polypropylene in the background

Closeup of nonwoven polypropylene fabric
Figure 1. The characteristic diamond-shaped, dimpled pattern seen in spunbond NWPP.

 

Mask Material Identification: Spunbond NWPP

Some sources of spunbond NWPP (e.g., bags constructed from 100% Spunbond NWPP) may be identified by either a tag indicating “100% Polypropylene,” or the recycling “#5 PP” indicator. In addition to material composition, it is important to identify the spunbond nonwoven structure of the material. This can be accomplished by looking for the characteristic diamond-shaped dimpled pattern.

TOP CHOICES: Reusable Grocery Bags (typically 70 – 100 gsm)

Spunbond NWPP grocery bags are designed to be in contact with food and have a greater consistency in material properties, manufacturing, and safety than materials used for things like craft projects and landscaping. Since they are designed to carry food, they have minimal particle shedding, and are designed to withstand washing and/or disinfection. Spunbond NWPP materials provide a balance of water-resistance, mechanical filtration, and breathability. Although NWPP bags are thicker than many materials, they work well as mask layers (especially outer layers).

  • NOTE: Do not use bags that are finished with a laminated waterproof coating or bonded to insulation as these may compromise breathability.
  • NOTE: Spunbond NWPP Conference Bags (typically 60 – 90 gsm) may also be considered: The material weight of conference/promotional bags is more variable than that of reusable grocery bags, and often includes lighter weight and/or softer materials.
<strong>Deeper Dive: </strong>Characteristics of polypropylene in reusable bags

“Isotactic polypropylene [all the methyl groups are lined up on the same side of the polymer chain] is generally used for commercial purposes due to its high melting point; its ability to withstand heat makes for a better alternative to plastic. This heat-resistant polymer is beneficial for reusable grocery bags, which are expected to carry items of varying temperatures. Polypropylene falls under the category of thermoplastics, meaning it can be softened and molded when it is heated while retaining its structure and durability. Polypropylene naturally repels water, therefore making grocery bags easy to clean. A material that can be easily disinfected is especially important since reusable bags are often exposed to bacteria when carrying raw foods. A review done on the spun bonded process acknowledges isotactic polypropylene as the most economically efficient material, as it is the most cost effective and produces the most fibers per kilogram (Lim 2). Since the order of the fibers doesn’t matter, more fabric is yielded as all the material ends up getting pressed together (Kansal 9).”

TOP CHOICES: SmartFab Backgrounds (typically 65 – 70 gsm)

Smartfab Backgrounds (aka doubleweight) is 65 to 70  gsm crafting material constructed from 100% NWPP. Recent laboratory testing of multi-layer Smart-Fab samples and mask prototypes suggest that it may be a good choice for use in community masks based on its performance relative the ASTM F3502 barrier face covering standards.

Summary Bar Graphs of Mask Testing Results

CAUTION:

Safety and usability of NWPP from alternatively sourced materials cannot be assumed. Special caution is recommended advised when considering meltblown NWPP, fusing interfacing, landscaping materials, surgical barrier materials, and crafting materials.

Materials Selection FAQ

Is all non-woven polypropylene the same?

NO. As with all textiles, there are different thicknesses and grades of NWPP. This is one of the reasons that we can’t guarantee or vouch for the effectiveness of hand-made masks from alternatively sourced materials.

How do I evaluate whether my non-woven polypropylene will work for a mask?

When you flick water at the fabric, you want to see the water droplets bead up and roll off, while the inside stays dry. You also want to make sure that the material is breathable. If it passes both of those tests, that is the evidence you are looking for that it will make a better-than-better-than-nothing mask.

What about meltblown NWPP?

Meltblown NWPP may pose inhalation risks. Meltblown NWPP tears easily, is harder to sterilize, lacks the diamond pattern, and is not used in reusable NWPP grocery bags. Although melt-blown is made from the same raw stock as spunbond NWPP, the structure of the material, and the size of the fibers are different. The individual fibers of melt blown NWPP are both shorter and thinner, which increases the risk of particle inhalation. For large-scale commercial mask operations with appropriate manufacturing controls and oversight, these risks can be mitigated; however, for home sewists the use of meltblown NWPP is not generally recommended at this time due to potential for occupational exposure while cutting, sewing, handling, and constructing unfinished meltblown materials.

What about interfacing?

NWPP interfacing that contains adhesives should not be used in DIY masks. Although interfacing without adhesive (e.g., sew-in interfacing) may ok for use, NWPP in interfacing is frequently made using different manufacturing processes and standards than the spunbond NWPP in reusable grocery bags. Its suitability for use as droplet protection in masks is under investigation.

What about landscaping cloth and geotextiles?

NWPP from landscape cloth and other geotextiles may pose inhalation risk. The fibers in these materials are prone to shedding and may pose risk of mechanical irritation when inhaled. In addition, preliminary data from particle testing suggests poor filtration performance, and they are not always water resistant.

What about surgical barrier materials?
[Added: May 17, 2020] In nonwovens used as barriers in other medical applications like gowns and surgical drapes, water-resistance and water-repellence may be achieved by chemically treating or coating the materials. These treatments allow materials to gain regulatory approval at higher barrier standards but may not be suitable for use in masks. Check manufacturers’ information on materials used for possible hazards (Jones, 2005).

What about vacuum cleaner bags? I read that they are great at filtering.

As this paper showed, vacuum cleaner bags are very good at filtering, but they have a higher pressure drop, meaning they aren’t particularly breathable. We recommend sticking to more breathable options, especially for well fitted mask designs.

What about 'Oly-fun'?

Many sites list ‘oly-fun’ as 65 gsm 100% NWPP. It’s suitability for use in masks is under investigation and discussed in greater detail in the finding and selecting polypropylene for masks post linked below. Preliminary results suggest it’s performance may be similar to that of SmartFab Backgrounds.

What about olefin?

Olefin is typically a mixture of polypropylene and polyethylene, which significantly lowers the melting point of the material. This material will melt/ shrink when boiled and should not be used in MakerMask designs.

What about nonwoven polyethylene?

The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (221 to 239 °F), which makes it unsuitable for proposed disinfection procedures.

Material showing air flowing through it

2. Breathability

Breathability is an important factor in face mask design and materials selection. Unfortunately, the materials that most effectively block droplets and particles typically have poor breathability, fit, and usability. Preliminary breathability checks for novel masks/materials frequently begin with qualitative functional assessments from developers and users. However, quantitative analysis of breathability, including tests of the pressure drop across the mask and CO2 accumulation, are important for verifying usability. For masks designs that are not focused on creating a tight seal/fit to the face (e.g. pleated masks), both air and CO2 can leak around the edges of the mask. For ‘fit tested’ masks with good face seals and submicron particle filtration requirements, these breathability measures become critical for the usability and success of the mask.

Fabric Layering Combinations

Research on the optimal number of NWPP layers is ongoing, however preliminary laboratory data suggests that three layers of spunbond NWPP provides adequate breathability for fitted and non-fitted mask designs. Despite qualitative assessment to the contrary, masks with additional layers began to show decays in performance (e.g., increased pressure differential across the mask and suboptimal CO2 accumulation). The ideal number of layers of NWPP will vary depending on the individual materials used and the trade-off between usability, breathability, particle filtration, and intended duration of use. Optimization and evaluation of prototypes, materials, and designs is ongoing.

Update: New guidance from the WHO recommends 3 layers (June 5, 2020)

New guidance from the WHO (June 5, 2020) recommends masks consisting of 3 layers including a combination of both hydrophilic and hydrophobic layers. For details see post about updated guidelines.

Is Halyard H600 Surgical Wrap breathable?

Active Question: Do masks made from Halyard H600 Surgical Wrap meet breathability standards? Masks made from H600 are gaining traction in medical communities and the benefits of H600 are indisputable: it has great particle filtration data, it is sterilizable, and is commonly available in hospital settings. However, uncertainty surrounding quantitative assessments of the breathability and the statements from Halyard disavowing the off-label use in masks suggest a cautious approach may be merited.

Edit: November 23, 2020. Two recently released publications (November, 2020) evaluated the breathability of H600 sterilization wrap, and both concluded that H600 is not recommended for use in masks because the breathing resistance is too high:

  • Grigg SE, Zampiron A, Akbaridoust F, et al. Are surgical masks manufactured from sterilisation wrap safe? [published online ahead of print, 2020 Nov 19]. Infect Dis Health. 2020;doi:10.1016/j.idh.2020.11.001. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7674969/ 
  • Sousan S, Garcia N, White A, Balanay JA. Filtration Efficiency of Surgical Sterilization Fabric for Respiratory Protection during COVID-19 Pandemic [published online ahead of print, 2020 Nov 6]. Am J Infect Control. 2020;S0196-6553(20)30974-3. doi:10.1016/j.ajic.2020.11.005 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7647410/ 
<strong>Did you know?</strong> Electrostatic treatments and breathability

Without electrostatic treatment, most materials that have 1um or better filtration compromise breathability. This is why the materials with the best particle filtration are often ill-suited for use in DIY masks. The special melt-blown filter materials that are used in N95 masks to get great filtering require special treatments (e.g. Corona Treatment or Electret Treatment) to achieve optimal particle filtration performance. More information on medical mask production.

CAUTION: DO NOT USE.

The following materials do not have sufficient breathability for use in DIY masks: Laminated waterproof bags, Evolon, Vacuum Cleaner Bags, HEPA Filters, et al.

3. Droplet Resistance

According to the CDC, droplets >5 μm in size have been implicated in transmission of influenza virus, adenovirus, rhinovirus, and SARS-associated coronavirus (SARS-CoV). For additional information about droplet precautions, see the official CDC guidance. In the context of face masks: “Fluid resistance is defined as the ability of a facemask’s material construction to minimize fluids from traveling through the material and potentially coming into contact with the user of the facemask.”

Fluid Resistance

Fluid resistance helps reduce potential exposure to blood and body fluids caused from splashes, spray or spatter [Infection Control Today, 2003].” For FDA-regulated medical masks, fluid resistance is measured as the “Resistance to Penetration by Synthetic Blood…as specified in Test Method F 1862.” Although this test is performed using synthetic blood, it is the generally used to establish the fluid resistance of masks such as those used for droplet protection [ASTM F1862 / F1862M – 17; Midha et al, 2012].

[Update: October 14, 2020] MakerMask had 40 samples of 3-layer spunbond NWPP tested according to ASTM F1862 fluid resistance testing standards. Our samples passed at a level higher than we anticipated (ASTM Level 2). Click here for details and the full report Fluid Resistance.

Home test of water resistance of mask materials
Figure 2. Home test of water resistance, evaluating the amount of water transferred across each fabric over a 60 second time course with 5 ml water applied to each material. Left to Right: Blue Shop Towel (cellulose based; 1.75 ml collected inside jar), Cotton (3.75 ml collected), NWPP shipping bag (midweight; 0 ml collected), and NWPP shopping bag (heavierweight, 0 ml collected). Note the visually observable differences between water atop hydrophilic materials and hydrophobic materials.  For details of this and other DIY home mask material testing download our DIY Face Mask Material Testing Guide.

Water Resistance

Information is available on the water resistance of spunbond NWPP materials such as those used in MakerMask designs. Spunbond NWPP is naturally hydrophobic (water-repellent).

DIY Home Test for Water Resistance
  • A quick qualitative assessment, a ‘flick’ test, can be performed to see if water beads up on the surface of the material (suggesting it is hydrophobic), or if it saturates into the fabric (suggesting it is hydrophilic).
  • Quantitative assessment of the passage of water through mask materials over a given interval of time (e.g. 60 seconds or 1 hour) can be conducted by mask developers and users at home.

 

Pot of Boiling water for disinfection of fabric masks made with nonwoven polypropylene

4. Disinfection

[Update April 11, 2020] Click here for our post with research and details on mask cleaning and disinfection methods

The fourth key factor for MakerMask designs is whether or not the full mask can be disinfected before use. The current recommendation for home use is to boil masks for 10 minutes prior to use. This procedure was established because “boiling is sufficient to kill pathogenic bacteria, viruses and protozoa (WHO, 2015)”. The duration maximizes disinfection of all of the mask layers. Boiling as a standardized home disinfection method provides a consistent, maximum temperature well below the melting/deformation point of the 100% spunbond NWPP typically used in reusable grocery bags.

<strong>Deeper Dive</strong> into the melting point of spunbond NWPP

The melting point of polypropylene occurs in a range. 100% NWPP used in high-quality re-usable grocery bags/conference bags is primarily isotactic polypropylene, which has a melting point between 160 to 166 °C (320 to 331 °F) and is safe to boil (100 °C / 212 °F), steam (121 °C / 250 °F), and/or autoclave. Industry guidance for decorating spunbond NWPP tote bags (for groceries/conferences/promotional purposes) suggests that, “bags should not be pressed any higher 275 degrees without experiencing some melting of the fabric. Some transfers that heat at 300 degrees may be used, however some bags may experience minor melting at this temperature.” NOTE: The use of pressure cookers for steam sterilizing masks (up to 121C / 250F) has been suggested, but this method of sterilization remains untested/unverified at this time.

Although additional disinfection procedures have been proposed, they have not all been evaluated for this purpose. In general, harsh chemicals (e.g., bleach) are not recommended as residual chemicals in the mask may cause unintended inhalation risks. In addition, oxidizing chemicals may cause the mask materials to degrade more quickly. The longevity of use of community spunbond NWPP masks is currently under investigation.

While awaiting more quantitative evaluation, two qualitative indicators indicate reduction of the functional characteristics of the mask:

  1. Water-resistance, when water stops beading on the surface during the ‘flick’ test, the droplet protection is degrading and the mask should be retired,
  2. Shedding, when the bonding of the fibers to the mask starts to degrade and the material starts shedding, the mask should be retired from use as dislodged threads could act as lung irritants (NOTE: landscape cloth and other geotextiles typically fail this assessment prior to first use).

Washing and Disinfection FAQ

Washing Masks with Polypropylene, cute words, and infographic

How do I wash non-woven polypropylene?

Although hand washing and hang drying is preferred, spunbond NWPP fabric can be machine washed (warm) and hung to dry. Rinse thoroughly, and do not use fabric softener. Avoid using bleach or alcohol on these fabrics, because those chemicals break down the properties that make NWPP a good choice. Before use, MakerMask masks can be disinfected with boiling water or in hospital autoclaves.

NOTE: If washing masks with soap or detergent, be sure to rinse thoroughly as soap residues may compromise water resistance.

[Update May, 2021] Click here for our post with general information about washing masks containing spunbond NWPP.

Should I iron the mask? What about while I'm making the folds?

NWPP has been known to melt with some irons and could damage both the mask and your iron. For this reason, we do not recommend ironing.  If you do, use precautions for sensitive/delicate fabrics such as ironing on the lowest heat setting and placing a towel or other cloth between the mask and your iron.

Should I disinfect my mask with a UV box?

It is important to note that ultraviolet irradiation methods are “unlikely to kill all the viruses and bacteria” in face masks with multiple layers, pleats, and/or seams. UV is not recommended for disinfection of multi-layer masks.

Should I heat my mask in a dry oven at 70C to disinfect my mask?

Dry heat is not recommended for MakerMask designs. Although some studies have shown that particle filtration efficiency remain OK with that dry heat at temperatures of 70°C for 30 minutes, the effectiveness of that temperature and duration of dry heat is less clear. It may be hot enough, for long enough to kill COVID-19, but the research suggests it may not be effective for killing other pathogens (e.g. bacteria) that may be growing on the mask. It is important to note that for dry heat sterilization the required temperatures are more than double 70°C, and the required times are also doubled.

Furthermore, dry heat sterilization is less effective than moist heat sterilization, and dry heat sterilization is not generally recommended for polypropylene. According to the CDC, “Dry-Heat Sterilizers: This method should be used only for materials that might be damaged by moist heat or that are impenetrable to moist heat (e.g., powders, petroleum products, sharp instruments). The advantages for dry heat include the following: it is nontoxic and does not harm the environment; a dry heat cabinet is easy to install and has relatively low operating costs; it penetrates materials; and it is noncorrosive for metal and sharp instruments. The disadvantages for dry heat are the slow rate of heat penetration and microbial killing makes this a time-consuming method. In addition, the high temperatures are not suitable for most materials. The most common time-temperature relationships for sterilization with hot air sterilizers are 170°C (340°F) for 60 minutes, 160°C (320°F) for 120 minutes, and 150°C (300°F) for 150 minutes. B. atrophaeus spores should be used to monitor the sterilization process for dry heat because they are more resistant to dry heat than are G. stearothermophilus spores. The primary lethal process is considered to be oxidation of cell constituents.”

CAUTION:

NWPP materials used for crafting, sewing, and other purposes may melt even though they are listed as 100% polypropylene because these materials are frequently composed of less crystalline forms of PP with melting points closer to 130 °C (266 °F). Although these materials may be washable, they may deform and/or melt when boiled, ironed, steamed, or autoclaved.

 

Final Thoughts on Spunbond NWPP

Some of the benefits of spunbond NWPP include that it is: commonly available in non-woven grocery bags and conference bags, hypoallergenic, water-resistant, conducive to mechanical filtration, and can be disinfected by boiling. Potential drawbacks of community-sourced spunbond NWPP include difficulties identifying suitable materials and variability in NWPP density and structure. These drawbacks can be mitigated by sourcing from more homogeneous subsets of spunbond NWPP based on use case. For example, reusable grocery bags are designed for the same use (carrying loads of food), have more consistent standards for strength, durability, quality, disinfection, and higher melting points than NWPP from other sources.

[Edit: June 26, 2020] For additional information about testing mask materials check out: 3 Easy DIY Mask Tests

Photo: DIY Mask Testing Setup for Fabric Materials. Photo includes spunbond nonwoven polypropylene mask, teaspoons, scale, elastic band glass, and cotton ball

 

For information about “window masks” or “clear face covering” check out: “5 Key Considerations for Window Masks.”

Select References/Links

Additional References/Links
  1. CDC: Strategies for Optimizing the Supply of N95 Respirators: Crisis/Alternate Strategies, Health Care Provider use of non-NIOSH approved masks or homemade masks. Accessed at https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirators-strategy/crisis-alternate- strategies.html on March 15, 2020
  2. Dato, V. M., Hostler, D., & Hahn, M. E. (2006). Simple respiratory mask. Emerging infectious diseases, 12(6), 1033–1034. https://doi.org/10.3201/eid1206.051468. Accessed at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3373043/ and https://wwwnc.cdc.gov/eid/article/12/6/05-1468_article on March 12, 2020 (Figure Below)
  3. Rengasamy S, Eimer B, Shaffer RE. (2010) Simple respiratory protection–evaluation of the filtration performance of cloth masks and common fabric materials against 20-1000 nm size particles. Ann Occup Hyg. 2010;54(7):789–798. doi:10.1093/annhyg/meq044. Accessed at https://pubmed.ncbi.nlm.nih.gov/20584862-simple-respiratory-protection-evaluation-of-the-filtration-performance-of-cloth-masks-and- common-fabric-materials-against-20-1000-nm-size-particles/ or https://academic.oup.com/annweh/article/54/7/789/202744 on March 12, 2020. “Fabric materials may provide some level of protection against the transmission of infectious aerosols when used in combination with other protective measures.”
  4. Institute of Medicine. 2006. Reusability of Facemasks During an Influenza Pandemic: Facing the Flu. Washington, DC: The National Academies Press. https://doi.org/10.17226/11637. Accessed at https://www.nap.edu/read/11637/chapter/6#62 on March 12, 2020
  5. Van der Sande, M., Teunis, P., & Sabel, R. (2008). Professional and home-made face masks reduce exposure to respiratory infections among the general population. PloS one, 3(7), e2618. https://doi.org/10.1371/journal.pone.0002618, Accessed at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440799/
  6. Mueller et al (2018). The effectiveness of respiratory protection worn by communities to protect from volcanic ash inhalation. Part I: Filtration efficiency tests. International Journal of Hygiene and Environmental Health Volume 221, Issue 6, July 2018, Pages 967-976. Accessed at: https://www.sciencedirect.com/science/article/pii/S1438463917308003
  7. Davies A, Thompson KA, Giri K, Kafatos G, Walker J, Bennett A. Testing the efficacy of homemade masks: would they protect in an influenza pandemic?. Disaster Med Public Health Prep. 2013;7(4):413–418. doi:10.1017/dmp.2013.43 Accessed at https://pubmed.ncbi.nlm.nih.gov/24229526-testing-the-efficacy-of-homemade-masks-would-they-protect-in-an-influenza-pandemic/
  8. Adam Burgess Mitsutoshi Horii (2012). Risk, ritual and health responsibilisation: Japan’s ‘safety blanket’ of surgical face mask‐wearing. Sociology of Health and Illness 34(8) 1184-1198. https://doi.org/10.1111/j.1467-9566.2012.01466.x, Accessed at: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1467-9566.2012.01466.x
  9. Advice on the use of masks1 in the community setting in Influenza A (H1N1) outbreaks. https://www.who.int/influenza/preparedness/measures/Adviceusemaskscommunityrevised.pdf
  10. Non-occupational Uses of Respiratory Protection – What Public Health Organizations and Users Need to Know. https://blogs.cdc.gov/niosh- science-blog/2018/01/04/respirators-public-use/
  11. How do respirators actually work? https://www.uvex-safety.com/blog/how-do-respirators-actually-work/
  12. Can DIY homemade masks protect us from coronavirus? https://smartairfilters.com/en/blog/diy-homemade-mask-protect-virus-coronavirus/
  13. What are the Best Materials for Making a DIY Face Mask? https://smartairfilters.com/en/blog/best-materials-make-diy-face-mask-virus/
  14. DIY masks: Is paper towel effective at blocking viruses? https://smartairfilters.com/en/blog/paper-towel-effective-against-viruses-diy-mask/
  15. Spunbond nonwoven Polypropylene Materials
    1. https://www.superiorfelt.com/products/air-filtration-media/sub-micron/personal-protection/
    2. https://blogs.cdc.gov/niosh-science-blog/2009/10/14/n95/
    3. Medical Face Mask Machine: The Complete Guide for the Medical Masks Production. https://www.testextextile.com/fighting-the-coronavirus-top-6-knowledge-to-know-before-investing-in-establishing-disposable-medical-mask-production-lines/ , “The core material of medical masks is polypropylene melt blown non-woven fabric after electret treatment. The filtering mechanism of medical masks is Brownian diffusion, entrapment, inertial collision, gravity sedimentation and electrostatic adsorption. The first four are physical factors, that is, the characteristics of the non-woven fabric produced by the melt blown method, the filterability is about 35%; this is not up to the requirements of medical masks, we need to electrotype the material and let the fiber Charged and used static electricity to capture the aerosol where the new coronavirus is located.”
    4. https://www.slideshare.net/muralikrishnan71697092/respiratory-protection-face-masks-and-respirators
  16. Non-woven Polypropylene In Masks: Links
    1. Example (https://www.nonwovenproductsupplier.com/products/3Ply-Nonwoven-Face-Mask.html): 1st ply: 20g/m2 spun-bond PP, 2nd ply: 25g/m2 melt-blown PP (filter), 3rd ply: 25g/m2 spun-bond
    2. Nonwoven polypropylene fabric usages (https://www.pp-nonwoven.com/medical-fabric-use-face-mask_p358.html):
    3. https://www.smartbags.co.uk/blog/bag-for-life-fabric-explained-non-woven-polypropylene-nwpp
    4. Non-woven: https://www.greatlakesfilters.com/non-woven-textiles/

17. NWPP Sterilization/Disinfection Information

  1. Ozone & Polypropylene: https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/other-methods.html
  2. https://www.cdc.gov/infectioncontrol/pdf/guidelines/disinfection-guidelines-H.pdf
  3. https://www.hmcpolymers.com/uploads/files/resources/hmc-pp-chemical-resistance.PDF, “Polypropylene offers good resistance tonon-oxidizing acids and bases, fats and most organic solvents; The melting point of polypropylene is 160°C / 320°F; Low temperature threshold: polypropylene becomes brittle below 0°C; NOT compatible with strong oxidants. According to ASTM D570, its 24 hr water absorption rate is 0.03%. It resists most strong mineral acids and bases, but, like the other polyole-ns, it is subject to attack by oxidizing agents. PP resins are appreciably affected by chlorosulfonic acid and oleum at room temperature, 98% sulfuric acid, 30% hydrochloric acid, and 30% hydrogen peroxide at 100°C (212°F).”
  1. https://www.industrialspec.com/resources/plastics-sterilization-compatibility/, “Steam Sterilization, also known as autoclaving, involves generating or injecting saturated steam into a pressure chamber at a temperature range of 121-148 °C (250-300 °F) at 15psi for a period of time sufficient to provide sterilization.
  2. Additional References: Alariqi SAS, Mutair AA, Singh RP (2016) Effect of Different Sterilization Methods on Biodegradation of Biomedical Polypropylene. J Environ Anal Toxicol 6:373. Doi: 10.4172/2161-0525.1000373, https://www.omicsonline.org/open- access/effect-of-different-sterilization-methods-on-biodegradation-of-biomedicalpolypropylene-2161-0525- 1000373.php?aid=73845

18. Materials

  1. “Allergy proof bedding with the smallest pore size will always be all polyester. All cotton allergy-proof bedding will have a larger poresize but will still be an effective allergen barrier. Cotton/polyester blends are in the middle when it comes to pore sizes. Dust mite fecal matter and/or body parts (we don’t actually breathe in whole dust mites) are as large as 10 microns. Pet allergen and mold spores are about 3 microns. In order for a microfiber mattress encasing to be effective against dust mites, it needs a pore size of 10 microns or less.” https://allergystore.com/blogs/news/what-does-pore-size-mean-in-allergy-proof-bedding
  2. Evaluation of materials used for bedding encasement: Effect of pore size in blocking cat and dust mite allergen.https://www.jacionline.org/article/S0091-6749(99)70495-1/fulltext
  3. 4 Pack Pillow Protectors Standard 20×26″ Hypoallergenic 100% Cotton Sateen Tight Weave 3-4 Micron Pore Size High Thread Count400 Style Zippered White Hotel Quality Non Noisy (4 Pack Standard Zip)
  4. Opinion: Evolon is 1um, but has too much impedance to air flow to use as a mask (fails breathability)
  5. Allergy Proof Bedding (Pore Size 1 to 6 micron, tested in some cases)

Spunbond nonwoven polypropylene sources; do use 100% NWPP grocery bags or conference bags. Don't use landscaping fabric or materials with coatings.

The Big Four: Criteria for Fabric Mask Materials for COVID
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